Variable voltage transformer



A. E. SNOWDON VARIABLE VOLTAGE TRANSFORMER March 21, 1961 2 Sheets-Sheet1 Filed April 27, 1956 INVENTOR. A/ZMME (5 /70 Wdon A TTORNE Y6 March21, 1961 A. E. SNOWDON 2,976,476

VARIABLE VOLTAGE TRANSFORMER Filed April 27, 1956 2 Sheets-Sheet 2INVENTOR. Ar'zfwr" E. Jnowdon BY WMK ATTORNEYJ VARIABLE VOLTAGETRANSFORMER Arthur E. Suowdon, Bristol, Conn., assignor to The SuperiorElectric (30., Bristol, Conn., a corporation of Connecticut Filed Apr.27, 1956, Ser. No. 581,107

6 Claims. (Cl. '32343.5)

The present invention relates to an alternating current voltagetransforming device, and more particularly to a variable or adjustabletransformer or potential converter.

In variable voltage transformers, it is common to pro vide acoil onwhich a sliding contact rides in electrical engagement with the turnsthereof for varying the output voltage. To assure electrical connectionwith the winding through all positions of travel of the brush, aplurality of turns of the winding generally have to be contactedsimultaneously by the brush. This creates a condition of short-circuitwithin the winding causing objectionable heating of the brush andresulting in a limitation on the magnitude of the energy which could betransformed.

"- I The heating at the brush is the product of the circulating currentand the voltage across the short-circuited turn. This latter isgenerally referred to as volts per turn and is found by dividing thevoltage across the whole winding by the number of turns. As greateramounts of power are transformed, more current flows through the brushand in order to maintain the heating of the brush to a safe value, thevolts per turn should decrease in proportion to the increase in current.However, transforming heavier current requires a large Wire size and todecease the volts per turn requires more'turns in the winding whichconsequently necessitates a larger core. As a result of suchproportionality factors and limitations, the use of variabletransformers for translating large amounts of power, i.e. in themagnitude of 10 k.v.-a. or more, has not been practical because of themagnitude of the equipment. Moreover, the present invention isapplicable to magnitude ofenergy of less than 10 k.v. a, since itmaterially reduces the required size of the core and coils witharesulting decrease in the cost of manufacture and the production of amore compact unit. It is, accordingly, an. object of this invention toprovide a variable voltage transforming unit for amounts of power havingdimensions not heretofore possible in which the volts per turn and theresulting brush heating is maintained at a safe value.

-It is another object of this invention to provide in a voltagetrans-forming unit of the type having two voltage transforming devicesconnected in series, one functioning to divide the initial supplyvoltage into substantially equal increments and the other device servingto regulate the desired portion of the increment which is included inthe output voltage of the unit, in which the switching from oneincrement to another is independent of the load current so that the loadcurrentis not conducted through the switching elements during theswitching operation. [It is a further object of this. invention toprovide in a variable voltage transforming unit of the above-disclosedtype having a regulating transforming device divided into, at least twoportions, in which the switching fromone portion of the regulatingdevice to the other does not re{ quire an instantaneous snap actionandalso in which the coils at the time of switching are substantially atthe same potential and so that sparking 'at the contacts is obviated.;;1t is another object of this invention to provide a varial" .1. if, iI r L United States Patent 0 ble voltage unit which is capable ofeffecting an extremely fine voltage regulation over an extended rangewith only a unidirectional movement of one control element required tovary the output voltage of the unit from the desired minimum to maximum.

A feature of this invention resides in having the input of atransformer, which may be either an autotransformer or an isolatedtransformer, connected to the AC. supply source and in which the outputof the transformer has a plurality of connections for dividing theoutput voltage thereof into potential increments. A commutating coilhaving a winding divided into two distinct coils wound. in the samedirection on a common core and the twocoils are selectively energized byswitch means from adjacent increments of the output of the transformer.A movable tap rides on the coils in electrical engagement with theconvolutions of the winding and forms one line of the output of thevariable voltage transforming unit while the other line is acontinuation of the supply source if the unit employs anautotransformer, or of the trans.- former output, if an isolatedtransformer is utilized.

When the movable tap is operating on the intermediate part of one of thecoils then the other coil is switched from one increment to the nextprogressively alternating increment in order to provide for step by stepadjustment of the output voltage of the unit between the desired minimumand maximum voltages. By utilizing such con: struction the volts perturn on the commutating coil is reduced to a value equal to the voltagein each increment divided by the number of turns in each portion of thecoil. For example, if there are ten increments, then the voltage perturn on the coil will be only one-tenth of the value encountered in thetransformation of a similar amount of electrical energy using only acoil of similar size with the same number of windings.

Other features and advantages of the invention will hereinafter appear.

In the accompanying drawing:

Figure 1 is a view partly in cross-section of the variable transformercomprising the present invention.

Fig. 2 is a partial view of the switching mechanism; and t Fig. 3 is aschematic diagram of the instant invention. The instant invention isshown in connection with'an autotransformer connectible to a source ofelectrical en: ergy and having its output connected to a commutatingcoil. A brush rides on the commutating coil for varying the outputvoltage of the device and switching means are utilized to connect thecommutating coil to various por tions of the autotransformer. Though anautotransformer is shownand preferred, an isolated transformer having aprimary and a tapped secondary may likewise be employed. i

Referring to the drawing, there is shown in-Fig 1 a variablevoltagetransforming unit comprising the invention and generallyindicated by the reference numeral 10: A base 11 has uprights 12attached thereto and a cover plate 13 is supported by the uprights. Inorder to maintain the coils in spaced relation within the framework}mounting blocks 14 engageable with the exterior surface of theautotransformer 15 are employed andsimilarly, mounting blocks 16maintain the commutating coil 17 in position. Both the autotransformer15 and the commutating coil 17 having laminated annular cores offerromag netic material, generally indicated by the reference numerals18 and 19 respectively. Toroidally woiundon these cores 18 and 19 arewindings 20 and 21,-20;being the autotransformer winding and 21 beingthe commuthe output voltage of the unit.

i shown, it is within the scope of this invention to employ motor drivenmeans if such were found desirable. A dial 26 is positioned on the topsurface of the cover plate 13 for cooperating with a pointer 27 mountedon the shaft 24 for giving a visible indication of the output voltage.The lower surface of the cover plate has a projection 29 which serves asa stop and cooperates with a stop arm 28 carried by the shaft 24 inorder to limit the rotational movementof the shaft.

Movement of the handwheel causes the output voltage of the unit to varyand this is accomplished by utilizing a commutating surface 30 on thecommutating coil 17. A brush 31 rides on the surface and is attached toan arm 32 which carries a slip ring brush 33 in electrical engagementwith a slip ring 34. The arm 32 at its other end is attached to a hub 36on the shaft 24 through an insulating ring 35. The hub 36 is freelyrotatable on the shaft 24 and carries a gear 37 which meshes with amating gear 38 rotatable on a pivot shaft 39. A small gear 40 is alsorotatable on pivot shaft 39 and is attached to gear 38 to cause movementof the latter. A driving gear 40a is fixed to the shaft 24 in order toprovide for movement of the arm 32. The ratio of the gears is dependentupon the number of contacts on the output of the autotransformer 15 forreasons hereinafter set forth, and in the instant embodiment with tencontacts the ratio is five to one, though of course with other numbersof contacts the ratio will vary therewith.

A switching mechanism, generally indicated by the reference numeral 41,is located axially of the cores and between them. While other switchingmechanisms such as relays, a traveling nut and the like may be used, thespecific embodiment of the switching mechanism shown is in the form oftwo axially aligned circular switch plates, a lower switch plate 42 andan upper switch plate 43. The two plates are maintained in spaced apartrelation by spacers 41a equally spaced about the periphery of the plates42 and 43. Support elements 41b are attached to the base plate 11 andthe plate 42 to hold the unit in position. Between the plates 42 and 43,a rotor 44 is located for rotary movement about the adjacent innersurfaces of the plates. The rotor carries a plurality of contacts and isconnected to the shaft 24 as by set screw 44a in order to be driventhereby.

Shown in Fig. 2 is a plan view of one of the switch plates and therotor. Each switch plate has three annular tracks 45. Each track,according to the desired sequence of switching, may have insulatingsegments 46 and conducting segments 47. The rotor 44 has contacts 48which move in these tracks to provide the necessary switching at allpositions of the handwheel 25 and arm 32. By reason of the foregoingstructure, movement of the handwheel 25 through an arc of aboutnine-tenths of a circle will vary the output voltage between its minimumand maximum output voltage and will move the rotor the same angulardistance but will cause rotation of the arm 32 approximately five timesas far in rotative travel or about four and one-half turns.

In Fig. 3 is shown the schematic diagram of the instart invention andcontains three components; the tapped autotransformer 15, the switchingmeans 41 and the commutating coil -17. The tapped transformer 15 isutilized to subdivide the input voltage into voltage increments and theswitching means 41 selectively connects each winding of the commutatingcoil 17 to alternating increments so that only the voltage of oneincrement is impressed across each winding. The values of the voltageincrements and the number of turns in each winding are such as to have asafe value of volts per turn on the winding. Thus if, for example, thenumber of turns in each winding is substantially different, then thevalues of voltage increments would likewise have to be substantiallydifferent in order to maintain a safe value of volts per turn. While thecommutating coil 17 may have more than two windings, the specificembodiment of the commutating coil 17 has two windings having an equalnumber of turns. Accordingly, in order to maintain the same value ofvolts per turn on each winding, the autotransformer 15 has ten taps;15-1, 152, 15-3, etc. for subdividing the input voltage intosubstantially equal increments. The number of taps employed involves amatter of choice depending on the value of the input voltage, thecurrent and the size of the coil 17. Though the taps have been shown asdividing the total input voltage from zero to 12.5% above input voltagemaximum, it is within the scope of the present invention to provide tapsonly on the portions of the winding of the autotransformer 15 whichcorrespond to the desired range of the output voltage of the unit '10.The input of the autotransformer 15 is through the leads 15a and 15b.

The winding of the commutating coil 17 is broken so as to provide two,independent yet substantially equal, coils 17a and 17b. Both of thesecoils are wound in the same direction on the core 19 and since thevoltage increments are equal they have substantially the same number ofturns. The winding 21 encompasses substantially completely the annularcore 19, i.e. throughout 360, so that there are no portions withoutturns and so that the brush 31 will at all times engage convolutions ofthe winding. The coil 17a has ends designated by a; and a while the endsof the coil 17b are b and b As previously set forth, the switchingmechanism in the specific embodiment disclosed is provided with trackshaving insulating segments 46 and conducting segments 47 Forillustration purposes in Fig. 3, in order to aid in the explanation ofthe device, the annular tracks are schematically shown as being straightand having insulating segments indicated by the reference numeral 46 andconducting segments shown symbolically by full line rectangles. Eachconducting segment is connected to one of the taps, 15-1, 15-2, 15-3,etc., and accordingly, are indicated by the reference numerals 47--1,47-2, 473, etc. to show to which tap they are connected. The rotorcontacts 48 are shown as shaded squares and since they are connected tothe ends a a b and b reference characters 48-a 48-11 48-b and 48-]1respectively are employed to indicate the contact which is connected tothe appropriate end.

With such a switching mechanism, the location of the insulatingsegments, the conducting segments and the moving contacts are such as tocause connections between the taps and the windings in the followingmanner. Initially, with the pointer 27 indicating the output voltage ofthe unit set at zero, the coil 17a is connected between taps 15-1 and15-2 by segments 47-1 and 47-2 being in engagement with contacts 48-aand 48-11 to ends a and a respectively. Fig. 3 illustrates this relationof the elements after the handwheel has been slightly moved from itszero position. Further rotation of the handwheel 25 causes the contactsto move upwardly on the tracks such that as the brush 31 approaches theends a b the contacts 48-b and 48-11 will be in engagement withconducting segments 47-2 and 47-3 respectively so that the winding 17bwill be energized by the voltage increment between the taps 15-2 and15-3. Both coils 17a and 17b are energized while the brush 31 is in theimmediate vicinity of the ends of the coils 17a and 17b and since thecontacts 48-11 and 48b are on the same segment 47-2, these ends of thecoils are at the same potential. Further clockwise movement of thehandwheel 25 positions the brush 31 on the coil 17b,

, reason of contacts 48-a and segment 47-3 and contact 48-a and segment47-4 being inengagement. With thebrush 31 adjacent the junction of theends a and b, the coils are energized, 17a by taps 15-3 and 15-4 and 17bby taps 15-2 and 15-3. For the output voltage varying from zero tomaximum, the coil 17a will be successively energized by the voltageincrements between the taps 15-1 and 15-2, 15-3 and 15-4, 15-5 and 15-6,15-7 and 15-8, and 15-9 and 15-10 while the coil 17b will be energizedby the voltage increments between the taps 15-2 and 15-3, 15-4 and 15-5,15-6 and 15-7, 15-8 and 15-9. The lower tap numbet is always connectedto the end a when the coil 17a is energized and to the end b of the coil17b when it is energized. Though the above structure increases theoutput voltage of the transforming device from zero to maximum as thebrush 31 is rotated clockwise, it

, will be apparent that rotation in the opposite direction woulddecrease the output voltage.

The output of the variable voltage unit 10 is positioned between lines53 and 54, the line 53 being connected to the tap -1 of theautotransformer 15, shown in the present embodiment, which is inactuality one line of the input to the unit, while the line 54 isconnected to the arm 32 which carries the brush 31 riding on thecommutating coil 17. If an isolated transformer is used the line 53.would be connectible to one output lead of the transformer; With thestructure shown, the coil 17 and the brush arm 32 carry the outputcurrent of the unit and this output would create difliculties at theswitching mechanism 41 when changing from one coil to the other. Inorder to obviate the problems which arise when the coil being switchedfrom one set of taps to the next carries the output current, the presentinvention provides for switching of one coil when the other coil is inthe output line. The switching is thus independent of the load, that is,the output does not pass through the switching means 41 at the time ofswitching the coils from one set of taps to another. Additionally, sincethe coils are wound in the same direction on the core 19 and since onecoil is energized while the other is being switched there is no sparkingat the switch contacts. This is so by reason of having an induced in thecoil 17b, for example, when the arm 32 is operating on the coil 17a,which opposes the voltage in the increment and is substantially equalthereto with the consequent result that there is substantially novoltage difference therebetween and hence no sparking occurs at thecontacts of the switching mechanism 41. The same effect occurs in thecoil 17a when the arm is operating on the coil 17b.

As shown in Fig. 3, the turns of the coils 17a and 17b are substantiallyadjacent each other, thus at certain positions of the arm 32, the brush31 may be in contact with one or more turns of the coil 17a and one ormore turns of the coil 17b. By the present invention of having bothcoils energized there is no break or interruption in the output of theunit when the brush 31 changes from one coil to the other. Moreover, thepresent invention obviates the necessity of having instantaneousswitching when changing from one coil to the other. With instantaneousswitching, it is apparent that if the desired voltage output is of sucha value as to require the brush to be located at either of these twojunction points on the winding 17, there would be a resulting constantswitching back and forth or hunting from one coil to the other withconsequent detrimental result thereto. According to the presentinvention, when the brush 31 is operating on one coil and as itapproaches the junction of the ends of the coils, the other coil isenergized so that both windings are energized when the brush is in theimmediate vicinity of the junctions. This is accomplished by having bothcoils 17a and 17b wound on the same core and in the same direction andhaving the cur rent (i.e., instantaneous values thereof beingconsidered) 6 flow in the coil in the same direction so that themagnetic flux produced thereby is additive. The effect of suchconstruction is to make a single autotransformer of the commutating coil17 and to impress on it the voltage between two adjacent taps. Forexample, with the brush 31 on the coil 17a and adjacent the end b of thecoil 17b, both a and b are connected to the same tap on theautotransformer 15.

From the foregoing, it will be appreciated that there has been discloseda variable voltage transforming unit capable of translating electricalenergy which is of a compact, practical and economical size as comparedto similar units for transforming the same amount of energy and yetwhich overcomes heating of the movable brush element above a safe value.A first transforming device breaks down the output voltage intosubstantially equal increments and then a second transforming devicehaving two substantially similar coils enables step by step energizationwith progressive alternate increments to provide for the variation inthe magnitude of the output voltage. The use of two similar coilspermits the switching of one coil when it is not being utilized in thecircuit with the advantages of no sparking at the contacts, independencefrom the load current and the obviating of a complex instantaneousswitching arrangement.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. A variable voltage transforming unit comprising a first voltagetransforming device having an output and an input connectible to asource of alternating current; means for providing voltage incrementsfrom the output; a second-voltage transforming device having a windingformed into at least two separate coils wound in the same direction on aclosed magnetic core; switch means for electrically connecting at leastone of the coils to an increment of the output of the first voltagetransforming device; a contactor for electrical engagement with a se--lective portion of the electrically connected coil; and, means, formingan output of the unit, connected to the: contactor and the first voltagetransforming device.

2. A variable voltage transforming unit comprising a. first voltagetransforming device having an output and an! input connectible to asource of alternating current; means for providing substantially equalvoltage increments from the output; a second voltage transforming devicehaving a winding formed into at least two similar, separate coils woundon a closed magnetic core in the same direction; switch means forelectrically connecting at least one coil to an increment of the outputof the first voltage transforming device; a contactor movable along thewinding and in engagement with the turns thereof; and means, forming anoutput of the unit, connected to the movablecontactor and the firstvoltage transforming device.

3. A variable voltage transforming unit comprising a first voltagetransforming device having an output and an input connectible to asource of alternating current; means for providing substantially equalvoltage increments from the output; a second voltage transforming devicehaving a winding formed into two similarly wound, independent coilswound on a closed magnetic core; a contactor movable along the windingin electrical engagement with the turns thereof; switch means forconnecting and disconnecting the coils to increments of the output ofthe first voltage transforming device and for disconnecting one coilfrom its increment of the output while the contactor is in engagementwith the intermediate portion of the other connected coil; and means,forming an output of the unit, connected to the movable contactor andthe first voltage transforming device.

4. A variable voltage transforming unit comprising a first voltagetransforming device having an output and an input connectible to asource of alternating current; means for providing substantially equalvoltage increments: from the output; a second voltage transformingdevice having a winding formed into two similar, independent coils woundon a closed magnetic core; a. contactor movable along the winding inelectrical, engagement with the turns thereof; switch means forconnecting and disconnecting the coils to increments of the output ofthe first voltage transforming device and for maintaining one coildisconnected from the output of the first voltage transforming devicewhen the movable contactor is in an intermediate portion of the othercoil; and means, forming an output of the unit, connected to the movablecontactor and the first voltage transforming device.

5. A, variable voltage transforming unit comprising a first voltagetransforming device having an output and an input connectible to asource of alternating current; means for providing substantially equalvoltage increments from the output; a second voltage transforming devicehaving a winding formed into at least two similar, independent coils,said coils being wound in the same direction on a closed magnetic core;a contactor movable, along the winding in electrical engagement With theturns thereof; switch means for causing connection of both coils todifferent increments of the output so that the magnetic flux caused byeach coil in the core is additive at at least one position of thecontactor; and means, forming an output of the unit, connected to themovable contactor and the first voltage transformingdevice.

6. A variable voltage transforming unit comprising a first voltagetransforming device having an output and an input connectible to asource of alternating current; taps for providing substantially equalvoltage increments from the output; a second voltage transformingdevicehaving a winding formed into at least two similar, independentcoils, said coils being wound in the same direction' on a closedmagnetic core and having at least one adjacent end portion; a contactormovable along the winding and in electrical engagement with the turnsthereof; switch means for connecting each coil to adjacent incrementswith the adjacent end portion of each coil being connected to the sametap; and means,. forming.

an outputv of the unit, connected to the contact and: the first voltagetransforming device.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent Na; 2 37m476March 21 1961 Arthur E. Snowdon It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 1, lines 42 and 45,, for "=k.v. a-" each occurrence read KV-acolumn 4, line 29 for "a read a column 8 line 20, list of referencescited, under UNITED STATES PATENTS, for "2572,1154" r d m. 2 5725 inSigned and sealed this 29th day of August 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer I Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION PatentN-d-w 2,97m476 March 21,, 1961 Arthur E. Snowdon It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below.

Column 1, lines 42 and 45,; for "k.V,'a each occurrence, read KV-acolumn 4, line 29 for "a read a column 8, line 20 list of referencescited, under UNITED STATES PATENTS for "25724454" read 2572 545 Signedand sealed this 29th day of August, 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

